I followed the all-grain recipe from page 98 of "Beer Captured" to the letter yesterday, yet recorded an OG of 1.047 instead of 1.059 as listed in the book. The ProMash program listed my efficiency at 79%.

I'm new to all-grain brewing (about 5 batches so far). My questions:

1. Would the OG be affected by the use of filtered water during mashing/sparging?

2. Is the target OG a ball park figure? How much deviation is acceptable?

With all-grain, there are a ton of factors that can affect yield. An efficiency of 79% isn't bad at all.

To answer your questions:

1 - No I don't think so, but water chemistry is a possibility. I wouldn't worry about that one.

2 - Any amount is acceptable...it's up to you as to what is acceptable. Any recipe book should be used as a starting point IMO, and you should make whatever changes sound fun. None of them ever end up being perfect clones in any event.

I wouldn't stress it...just add a bit more grain. As homebrewers, we can afford that solution. Cheers!

__________________Oh don't give me none more of that Old Janx Spirit
No, don't you give me none more of that Old Janx Spirit
For my head will fly, my tongue will lie, my eyes will fry and I may die
Won't you pour me one more of that sinful Old Janx Spirit